How do you edit and revise a novel?
Revise your novel from the top down. Start with the biggest issues and work your way down to the small details. Start with the structure, character motivation, conflict, pacing, and point of view. Then move on to individual scenes, dialogue, description, continuity, and grammar. You should take a break after completing the first draft so you can read your manuscript fresh. Other trusted readers or a professional editor might spot issues you haven't noticed.
How to revise a novel effectively
Revision isn't merely editing your work for grammatical correctness; it's about making your story clearer and more interesting. Be sure to wait until you have a fair portion of the novel written so that you can see the story in its entirety. Taking a break prior to beginning is also a good idea so that you can approach the project with fresh eyes.
Begin with the larger story
Summarize the novel briefly and then go through the journey of each important character. Is there a clear goal for your protagonist? Does the primary tension keep escalating? Is your conclusion the logical outcome of your story's events?
Identify missing turning points, subplots that aren't needed, character motivations that aren't strong, and areas that drag. These macro-level issues need to be addressed first before you begin editing individual sentences.
Work through the scenes
Each significant scene should have a purpose. What does your POV character want? What's preventing them from having it? How is the situation different by the time the scene ends? And why does this scene belong in this spot? Make the beginning of a scene stronger by providing the reader with some context or tension. You can often cut entrances, exits and conversations that don't bring anything new to the scene.
Improve the characters and the writing
Keep dialogue purposeful and give each character a unique voice. Not every conversation has to be high stakes. Use concrete description, and include details that fit the setting or characterize the POV.
Eliminate redundancies, and use action to imply the meaning when there is no reason for direct explanation. Vary the pace and length of sentences, and make sure the narrator's voice is uniform across the book.
Use feedback carefully
Try asking early readers to tell you about parts of the story they didn't like, or specific questions they had after reading. There's no need to take all suggestions seriously, but if many people share the same confusion over a certain point in the story, maybe there's a larger issue you need to address.
You may also want to hire a developmental editor for help with structure, or a copyeditor to attend to the language, consistency, and correctness of your prose. Once the larger changes are made, finish with a final proofread. Reading your work aloud, changing the format of your manuscript, and reading one chapter at a time will help you find the errors that previous rounds of editing missed.